This invention relates to distributed network systems in which a host computer is linked to a plurality of clients over a network for information interchange.
Systems are known in which a host computer is linked to a plurality of system clients over a network. In a typical configuration, a host server, termed a telnet server herein, is linked to a plurality of telnet clients via a multi-branch local or wide area network using the telnet protocol. At the host end of the system, the telnet server is coupled to the network via a transmission control protocol/internet protocol (TCP/IP) process which provides information transport services; while at each telnet client site a client is coupled to the network via a similar TCP/IP process. The telnet server functions to note requests for specified services from telnet clients and to service those requests. A plurality of application programs are provided at the host installation, and appropriate ones of these programs are selectively coupled to the telnet server in response to telnet client requests.
The procedure whereby a point-to-point link is established and information is exchanged between a host application and a telnet client application is termed a session, and a session typically commences by the generation of a service request by a telnet client at a client workstation. In response to the receipt of a request for service, the telnet server establishes a memory structure using host system memory for controlling the service procedure and for retrieving, storing and forwarding information pertaining to the request for service. For example, in a unix based system, the telnet server establishes atty unix structure and associated control buffers in response to the receipt of a request for a session. Typically, an authentication routine is initially called to determine whether the telnet client requester is authorized to participate in the requested service, with the routine typically providing the client user ID and password at the client workstation which is then checked by the telnet server at the host installation using an authentication application program routine. After the requester has been cleared by the authentication routine, the service requested is carried out in conjunction with the appropriate one or more application programs. Once the service is completed, the session is terminated.
During a session, either hardware or software failures (or both) can occur at the host location, at the client location or over the physical link therebetween. When such a failure occurs, the results of all session processing up until the time of failure are lost, and the session must be restarted from the beginning. This loss of session processing results is undesirable since valuable processing time is wasted and since the network must now be reoccupied for that additional length of time required to achieve that same stage in the service session prior to interruption of the link.